This invention relates to methods for anamorphically shaping and deflecting beams of electromagnetic radiation, for example, the light beam produced by a diode laser. More particularly, it relates to a method and apparatus for deflecting a beam by precisely 90.degree. while anamorphically altering its intensity profile.
The advent of the diode laser has greatly expanded the need to handle laser beams of elliptical cross section. Because these lasers have very asymmetric active regions, they may exhibit beam divergence ratios in the 1:2-1:4 range. When the beam is collimated by a collector lens, it retains its ellipticity. The beam ellipticity, in turn, affects (usually reduces) the efficiency with which the beam can be focused through a circular objective lens.
Heretofore, it has been common to use a Littrow-type prism (i.e., a three-sided right angle prism) for anamorphically expanding an elliptical beam to make it more circular. The output of a diode laser is predominantly polarized in the TE state, and the collimated beam is polarized parallel to its minor axis. If, as shown in FIG. 1, the beam is incident at the Brewster angle .theta..sub.B, on the hypotenuse face of a Littrow prism in which one of the acute angles is cut at the Brewster angle, it will be anamorphically expanded by a factor n in a direction of the minor axis, where n is the refractive index of the prism. While this is a good approach for reducing the ellipticity of a diode laser beam, it is disadvantageous from the standpoint that the beam is deflected by an inconvenient angle .alpha., where .alpha.=2.theta..sub.B -90.degree.. For ordinary glass prisms, .alpha. is about 23.degree.. For many applications, it is desirable that the expanded beam be either parallel to if not co-linear with, the incoming beam or, alternatively, be deflected during the expansion by some convenient angle, for example, 90.degree..